03-17-2009, 10:32 AM
| || |
I would suggest you replace the entire substrate. The two gravels will just keep mixing together, especially if you do partial water changes and syphon the substrate as you should. It is possible to change the substrate without removing the fish, but it is preferable to remove them to a temporary tank if you can. If you have an empty 10 or 20 g you could keep the fish in it for a day or two (use the filter from the 33g without washing or rinsing it), but you can still manage this in one go. I have, out of necessity in an emergency, completely reset a 115g and a 90g aquarium, each within one day, and they each contained about 100 fish.
A 10 g tank will suffice for the short amount of time; use the water from the existing tank and transfer the filter to the temporary tank, then net out the fish. Once they are out, gently pull up the plants (this will not hurt them) and lay them on the water (floating) in the temporary tank, drain the tank, remove the gravel, and replace it with washed gravel that you want. Partly (half or thereabouts) fill the tank with water at the correct temperature, add plenty of a good water conditioner (you can't overdose, but don't go to extremes). Ensure the pH is within a couple of decimal points of the existing water (e.g., ph 7.0 to 7.2, or 6.6 to 6.8 etc). Replant the plants. Again, do not clean the filter, as this will remove more bacteria. Use as much of the water in the temporary tank as you can, then net the fish back into the 33 and move the rest of the water from the temproary tank to the 33; top up with fresh (don't forget your water conditioner).